[HeartBeat Detection]
The heartbeat measurement technology that we chose for this project is the photopletismography. This technique is based on the use of a photodiodethat emits a light pulse in a specific wavelength which, after passing by the blood vessel, the wavelength signal captured by the photosensor changes.

According to that change, we can determine whether a pulse of blood has passed in a specific time, depending on our sampling rate.
[Stress Recognition]
Once the signal is taken, it is carried to the raspberry Pi using a proper wirebased connection to avoid any unwanted interaction with other signals and for a better performance of the device. Then, the Raspberry PI will process the data in real time and, at the same time, it will do a basic threshold based control for deciding whether the person is under stress or not. When this process recognize the stress, it makes beep sound for warning.